Kouichi Takeshita

A theoretical analysis of the Jahn–Teller effect in the photoelectron spectrum of methane

An analysis of the Jahn–Teller effect in the photoelectron spectrum of methane was performed by the use of the ab initio self‐consistent field and configuration interaction calculations. The molecular structures of the CH+4 ion, which have a local energy minimum, are found to be in the C2v and C3v symmetry. The vertical excitation energy is calculated to be 14.23 eV and the adiabatic ionization potentials of the CH+4 ion including zero‐point vibrational energy are estimated to be 12.25 and 12.68 eV for the C2v and C3v symmetry, respectively. We calculated the normal modes of vibration and the Franck–Condon factor in the harmonic oscillator approximation, and assigned the vibrational band below 13.10 eV of the CH+4 ion.

A theoretical study on the ionic states and the photoelectron spectra of difluoromethane (CH2F2)

Abstract Ab initio calculations have been performed to study the four low-lying ionic states, 2B2, 2B1, 2A1 and 2A2 of difluoromethane (CH2F2). The equilibrium molecular structure of these states is presented. The theoretical ionization intensity curve including the vibrational patterns is also presented and is compared with the photoelectron spectra of CH2F2 and CD2F2. A new assignment of the photoelectron spectra is proposed.

Theoretical study on the quasi-bound state and UV spectrum of H2O2 with inclusion of the vibrational structure

Abstract In order to assign the vibrational structure of the UV spectrum of hydrogen peroxide, we have performed ab initio calculatons at the SCF and CI levels and studied the potential energy surfaces of the lower excited states. The first 1 B and second 1 A states have a local energy minimum at the trans and cis conformations, respectively. The theoretical intensity curve including the vibrational excitations has been calculated using the harmonic oscillator potential model. A number of new assignments of the vibrational levels of the UV spectrum are proposed.

On the lower excited states of the formyl radical HCO

Abstract Extensive ab initio Cl calculations were carried out on the lower four doublet states of HCO. The results are used in assigning hydrocarbon flame bands, the upper state of the A and B bands being the B 2 A′ and C 2 A″ states. These two states are characterized as bonding of H with the π-to-π * state of CO.

A theoretical study on the ionic states and the photoelectron spectrum of dichloromethane (CH2Cl2)

Abstract Ab initio calculations are performed to study the molecular equilibrium structure and the vibrational level of the low-lying four ionic states, 2 B 2 , 2 B 1 , 2 A 1 and of dichloromethane (CH 2 Cl 2 ). The theoretical intensity curve obtained by the Franck-Condon factors for the ionization transitions are also reported and compared with the photoelectron spectrum of CH 2 Cl 2 . A number of new assignments of the photoelectron spectrum are proposed.

Molecular structure and conformation of 3-methyl-2-butanone: A gas electron diffraction investigation combined with ab initio calculation and vibrational spectroscopy

Abstract The molecular structure and conformation of 3-methyl-2-butanone (isopropyl methyl ketone) have been investigated by gas electron diffraction. Ab initio SCF calculations at the 4–21G level have been carried out and infrared and Raman spectra have been measured in order to obtain supplementary information for the structural determination. The skew conformer is the most stable with a relative abundance of 90(7)% and the eclipsed conformer is the next most stable. The important structural-parameter values of the skew conformer with the limits of error in parentheses are as follows: rg(CO) = 1.217(2) A, rg((O)CC)av = 1.525(1) A, rg((C)CC)av = 1.534(1) A, rg(CH)av=1.113(2) A, ∠αC3C2C4=118.0(8)°, ∠αO1C2C3=120.8(14)°, ∠αC2C3C5=108.0(10)°, ∠αC2C3C6=113.4(12)°, ∠αC5C3C6=111.7(21)°, ∠αHCHav=108.7(8)° and o1(O1C2C3H7)=140(4)°. The dihedral angel, o1, is defined as zero when the O1C2C3H7 fragment is eclipsed.

Theoretical study on the first broad band of the photoelectron spectrum of H2O2 with inclusion of the vibrational structure

Abstract Ab initio calculations at the SCF and CI levels have been performed to calculate the potential energy surfaces and stable conformations of the first two ionic states of hydrogen peroxide (H 2 O 2 + ). The lowest ionic state 2 B is found to be most stable in the trans conformation. The second lowest state is the 2 A state and is stable in the cis conformation. A theoretical intensity curve including the vibrational excitations has been calculated using the harmonic oscillator potential model. The agreement with the experimental photoelectron spectrum is satisfactory.

The conformation of 2-cyclopropylpropene and 1,1-dicyclopropyl ethylene by means of ab initio SCF calculations

Abstract The geometrical structure of 2-cyclopropylpropene and 1,1-dicyclopropyl ethylene has been determined by means of the ab initio SCF gradient method. The most stable conformation of 2-cyclopropylpropene has a gauche structure and the internal rotation angle between the cyclopropyl ring and the vinyl group is calculated to be 62°. The most stable conformation of 1,1-dicyclopropyl ethylene also has a gauche structure and the internal rotation angles between one of two cyclopropyl rings and the vinylidene group are 64°.

A theoretical study on the lonic states and the photoelectron spectra of dichlorodifluoromethane (CF2Cl2)

Abstract Ab initio calculations are performed to study the molecular equilibrium structure and the harmonic vibrational frequency of the low-lying four ionic states 2B2, 2A2, 2B1, and 2A1 of dichlorodifluoromethane (CF2Cl2). The theoretical intensity curve obtained from the Franck-Condon factors is in good agreement with the photoelectron, (PE) spectrum. The results show that the four maxima of the PE spectrum from the lower energy side correspond to the 2B2, 2A2, 2B1, and 2A1 states. Three vibrational progressions are found in the theoretical intensity curve of 2B2. Higher vibrational excitations to the ν4 (ClCCl bending) mode contribute to all progressions and vibrational excitations of the ν1 and ν3 modes also contribute to intensity.